Modification of a porous oxide layer formed on an Al–Zn–Mg alloy via plasma electrolytic oxidation and post treatment using oxalate ions

Abstract

This study investigated the surface modification of the oxide layer of an Al–Zn–Mg alloy via plasma electrolytic oxidation (PEO) followed by post treatment using oxalate ions. The samples were treated by PEO in alkaline-aluminate electrolyte with and without Na₂C₂O₄. The post treatment was performed additionally by immersing the PEO-treated sample into Na₂C₂O₄ solution. Upon PEO, the existence of oxalate ions would minimize the structural micro-defects. This was attributed to the formation of an oxalate-adsorption thin-film, generating soft plasma sparks after breakdown. Moreover, the oxide layer after post treatment using Na₂C₂O₄ solution exhibited the crack-free structure desirable for suppressing the corrosion rate.